Transmission system



A. L. FITCH.

TRANSMISSION SYSTEM.

APPLICATION FILED NOV. 26, 19H. RENEWED DEC. 26. 1918.

1,397,862, Patented Nov. 22, 1921.

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y flM UNITED STATES PATENT OFFICE.

ALBERT L. FITCH, OF EAST ORANGE, NEW JERSEY, ABSIGNOR TO WESTERNELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A COMORATION 'OF NEWYORK.

TRANSMISSION SYSTEM.

Application filed Kovember 26, 1917, Serial No. 203,949. RenewedDecember 26, 1918. Serial No. 288,420.

' for connecting a transmitter to an electron discharge device such as avacuum tube amplifier. Previous to this invention it has been proposedto connect a condenser transmitter to a vacuum tube amplifier, and alsoto use a single battery or source of electromotive force, both in theoutput circuit of the amplifier and as a means for polarizing thetransmitter.

A condenser transmitter of a well-known type consists of two-electrodes,one of which is conductively connected to an outer shell or casingusually made of metal. This casing is subject to being touched orotherwise accidentally or inadvertently grounded, thereby grounding theelectrode. Since, in the ordinary operation of a vacuum tube amplifierof the three-electrode type with a single battery as referred to above,the filament usually is grounded in order to secure good operation, anysuch accidental ground ing of the transmitter case would cause eitherthe battery or the condenser transmitter to be short-circuited and thusinterfere with the operation, as well as being a source of inconvenienceor danger. It is a particular object of my invention to remedy thisdefect by so relating the battery, which performs both the functions ofcharging the condenser and furnishing current to the output circuit,with circuits and apparatus that one. electrode of the condensertransmitter may always be grounded during normal operation. As the otherelectrode is insulated within the case, it is not likely to be grounded.While this invention is preferably used in connection with apparatus inwhich a common source of electromotive force polarizes the transmitterand operates the amplifier, it is not peculiar to such an arrangement,but, broadly stated, is directed to the combination of a condensertransmitter Specification of Letters Patent.

to function as an amplifier, is associated with the condensertransmitter conventionally dia'grammed at T, in which electrode t is-themovable or vibratory plate against which sound waves impinge and t isthe fixed electrode. We may assume that in this transmitter, theelectrode t is uninsulated from the metallic case a which contains itand also has its exterior surface exposed, while electrode 25 is mountedupon the interior of-the transmitter and is insulated, as represented bythe supporting insulation material -1. Plate 25 is connected to thefilament or cathode 2 of tube A by conductor 3, while plate t isconnected to grid or control electrode 4 by conductor 5, in which isplaced condenser C. Plate t is also adjustably connected to battery B atthe positive terminal by conductor 6, while conductor 3 is continued toconnect with the negative terminal of the battery B. A battery 7 isconnected between the grid and filament to keep them at a properrelative potential and an impedance in the form of the high resistance 8is connected in series with this battery. This resistance functions toprevent a" short circuit between the plates of transmitter T. Forsatisfactory operation, resistance 8 should be of such a value that theminute differences of fiuctuating potential existing across filament 2and grid 4, would not cause an appreciable flow of current throughresistance 8 in the time occupied by one complete fluctuation. In aparticular instance resistance 8 had a value'of one megohm. The plate oranode 9 of tube'-;A is adjustably connected through asuita'ble'conductor 10 to the positive terminal of battery B, which isthus in series in the output circuit of the tube A. A transcuit of anypart of the apparatus.

' either electrode may be grounded, it is preferred to ground the onewhich is most exposed. Condenser O is of large capacity so that itsimpedence is negligibly small in comparison with the input impedance ofthe amplifier A.

The parts of the multi-stage amplifier circuit of Fig. 2 correspond ingeneral to Fig. 1, andthe above description is applicable thereto exceptas mentioned. The battery B is also used as a source of direct currentin the plate-filament circuit, for a second amplifier A. The directcurrent of the plate-filament circuit of amplifier A passes from late 9to filament 2, through resistance 1 and battery B, while the alternatingvoltage is impressed across both of resistances 17 and 14:. Thevariations of drop in voltage across resistance 14 are impressed uponthe amplifying tube A and further amplified. The direct current path inthe output of A is from plate 9', through resistance 15 and battery B,to filament 2, while the amplified alternating current variations areimpressed upon a line 12 by a transformer 11 as in Fig. 1.

The disclosure herein of particular means for carrying out the inventionshould not I be interpreted to limit the invention to electrodes of saidcondenser at different relative potentials, and means for impressing thealternating current due to variation of the said capacity upon anamplifying device, said amplifying device being supplied with operatingcurrent by said source of electrical potential, said condenser havingone electrode thereof grounded through a path of negligible resistance,the characteristics of said path being such as to keep said electrode atground potential.

2. In combination, a condenser transmitter with an electron dischargedevice, one

tially ground potential.

terminal of the transmitter being permanently at ground potential and asource of electromotive force common to a circuit fy through thecondenser transmitter and the output'circuit of said device.

3. In combination, a transmitter for changing sound waves into waves ofelectrical current, an electron discharge device for'said current waves,a common source of electrical energy arranged to energize saidtransmitter and to furnish operating current for said device, and a pathfrom one terminal of said transmitter to ground, the characteristics ofsaid path being such that saiil one terminal is kept at ground potentiaL. In combination, two electrodes 'constituting a transmitter forchanging sound waves into waves .of electrical current, an electrondischarge device for said current waves, a common source of electricalenergy arranged for polarizing said transmitter and for furnishingvoltage to said device, one of said electrodes being grounded through apath, the characteristics of said path being such as to keep saidelectrode at substan- 5. In combination, a transmitter for changingsound waves into electrical waves, an amplifier for said electricalwaves, and a common source of electrical potential for polarizing saidtransmitter and supplying operating current to said amplifier, saidtransmitter having a terminal grounded through a conducting path, thecharacteristics of said path being such as to keep said terminal atsubstantially ground potential.

6. In combination, a transmitter for changing sound waves intoelectrical waves, a-vacuum tube, and a common source of electricalpotential for energizing said transmitter and supplying voltage to saidtube, a terminal of said transmitter having a ground connection, therebeing no conducting path through said ground connection from oneterminal of said transmitter to the other terminalthereof.

7. In combination, a device having two electr'odes which constitute anelectrical capacity, one electrode being free to vibrate, the vibrationsthereof causing variations of electrical capacity in said devicecorresponding to the said vibrations, a source of electrical energy forcharging said capacity, a conductor, and means whereby said vibrationsof electrical capacity cause a varying current in said conductor, anamplifier for said current, said source of electrical energy furnishingoperating current for said amplifier, one of said electrodes beinggrounded through a path whose nature is such as to keep said electrodeat ground potential.

8. In a device for transforming sound waves into amplified electricalwaves, a transmitter connected in series between two electrodes ofihnelectron discharge device, a comparativly high resistance forming ashunt circuit around said transmitter, and a second shunt circuitextending from a terminal of said transmitter through a source ofpotential to one of said electrodes, said source of potential also beingconnected serially in the output circuit of said electron dischargedevice.

9. Means for transforming sound waves into amplified electrical waves,including a transmitter connected in circuit with a source of electricalenergy and two elements of an electron discharge device, a resistanceexternal to said device connecting said elements, said source ofpotential being in a series circuit connecting one of said elements witha third element of said electron discharge device, and a conducting pathof negligible resistance from a terminal of said transmitter to ground,the characteristics of said path being such as to keep said terminal atground potential.

10. In a device for transforming sound waves into electrical waves ofconsiderable amplitude an electrostatic transmitter whose electrodes arerespectively connected to the filament and grid of a three-elementelectron discharge device having a grid, a filament and an anode; theconnection to said grid containing a condenser whose impedance isnegligible in comparison with the impedance of the input circuit of saiddevice, and a comparatively high resistance directly connecting saidfilament and grid, said electrode which is connected to. said grid beingconnected to said filament through a shunt circuit containing aresistance and a source of electromotive force, said source beinglocated serially in circuit with said filament and said anode of saidelectron discharge device. l

11. In combination, two electrodes constituting a transmitter forchanging sound waves into waves of electrical current, a

vacuum tube, a common source of electrical energy arranged forpolarizing said transvmitter and for furnishing voltage to said vacuumtube, one of said electrodes being grounded through a path having nosource of electromotive force contained therein.

12. In combination, a condenser transmitter having two electrodes, oneof said electrodes being connected to a cathode of an electron dischargedevice, the other of said electrodes being connected to a controlelectrode of said device, and means whereby a terminal of said cathodeand one of said condenser electrodes are maintained at ground potential.v

13. The combination with a vacuum tube having a source of voltage, of acircuit comprising a condenser transmitter, said source of voltage and ahigh resistance, said transmitter having an electrode connected toground through a low impedance path.

14. In an electric system, a clrcuit containing a source of voltage, acondenser transmitter having an electrode connected to ground through apath of negligible impedance, and means for impressing upon an outgoingline the electrica variations produced in said circuit by saidtransmitter.

15. In an electric system, a circuit containing a source of voltage anda transmitter having a pluralitypfelectrodes, one of said electrodesbeing connected directly to ground, means for impressing upon a secondcircuit containing said source of voltage the electrical variationsproduced in said first circuit by said transmitter.

16. A condenser transmitter having a plurality of electrodes, a metalliccasing, one of said electrodes being connected to said casing, a sourceof voltage, and a grounded connection between said source and saidcasing.

17. The combination with a vacuum tube, of a condenser transmitterhaving a plurality of electrodes, a metallic casing, one of saidelectrodes being connected to said casing, a source of voltage, agrounded connection between said source and said casing, and means forimpressing upon said tube the electrical variations produced in saidtransmitter.

In witness whereof, I hereunto subscribe my7name this 20th day ofNovember A. D., 191

ALBERT L. FITCH.

